Many off highway vehicles utilize a hydraulically powered brake system to provide braking of one or more wheels and/or axles. These systems typically consist of a hydraulic brake valve, brake pedals operated by the driver of the vehicle, and a linkage to transmit force from the pedals to the valve. In certain of such systems, the linkage includes a pin joint which transmits the force from the brake pedals to the pushrods, and the pushrods then press against a plunger which is part of the brake valve. Depressing the plunger actuates the brakes. A guide bushing keeps the pushrod in a mostly vertical orientation. The bushing, however, creates a pushrod motion such that as the top pin joint swings along an arc with the pedal. This causes the lower end of the pushrod to move horizontally as well as vertically, and the end of the pushrod slides or “scrubs” over the surface of the plunger, causing wear on both parts.
In addition, hydraulic systems can inherently have pressure ripple and vibration. This vibration can be transmitted from the brake valve, through the plunger and the pushrod to the pedals. Such vibration can generate noise or other inconveniences to an operator of the vehicle.
In John Deere self propelled sprayers, an additional extension spring is added to hold the pushrod off of the brake valve plunger when the brakes are not being applied. To do this, one end of the spring is fixed to a control support, and the other attached to the pushrod itself. An additional upstop is required to limit upward pedal travel due to this spring. Upon braking, the spring is stretched by the force applied to the pedals and pushrod, allowing the gap between the pushrod and brake valve to close, thus allowing the pushrod to depress the plunger. This design requires additional components (spring, mounting bracket, upstop for pedals) and the added resistance in the system which reduces the force delivered to the brake valve plunger because the extension spring counteracts some of the force applied by the operator.
A simple means to isolate the brake pedals and linkages from the hydraulic vibrations of the valve is desired.